A piece of outdoor concrete usually shrinks during hardening. This shrinkage is due to the evaporation of some of the water contained in the concrete. Cracking occurs when the shrinkage forces are greater than the strength of concrete. CSC) as we know it today was formed in 1958 by merging three premixed companies.
Although concrete is a very strong building material, it has its limits. Placing excessive amounts of weight on a concrete slab can cause cracks. When you hear that a concrete mix has a strength of 2000, 3000, 4000, or more than 5000 PSI, you mean the pounds per square inch it would take to crush that concrete slab. This category covers the performance of concrete whose shape can no longer be altered without damage.
It includes cracks caused by drying, shrinkage, as well as those resulting from temperature movements that take place in all materials exposed to the elements. Unless the structure in question allows movements of its limbs without developing excessive stresses, extensive cracks can often occur. Cracking cracks after hardening can result from excessive flotation that tends to attract water and cement to the surface, which then comprises weak concrete subject to high shrinkage stresses. More often, they are the result of poor curing.
Other cracks that occur after hardening can be caused by the lack of proper reinforcement in the corners, insufficient depth of concrete over the bends in the reinforcement, the nesting of reinforcing steel in concrete, the lack of expansion and contraction joints. Plastic Shrinkage Cracks Probably the most common reason for early cracks in concrete is plastic shrinkage. When concrete is still in its plastic state (before hardening), it is filled with water. This water takes up space and makes the slab a certain size.
As the slab loses moisture during curing, it becomes a little smaller. Because concrete is a very rigid material, this shrinkage creates stress in the concrete slab. As concrete shrinks, it crawls through its granular sub-base. This impediment to their free movement creates a tension that can literally separate the slab.
When the stress becomes too great for the now hardened concrete, the slab cracks to relieve stress. Especially in hot weather, shrinkage cracks can occur as early as a few hours after the slab has been poured and finished. Cracks in concrete are common and develop when stresses in concrete exceed its strength. Cracks are often caused by normal shrinkage of concrete as it hardens and dries.
Cracks in concrete can range from being non-structural and unsightly, to being detrimental to the structural integrity and safety of a building. This is the main cause of cracking in hardened concrete. This cracking occurs close to restrictions due to volume changes in concrete. When concrete is exposed to moisture, it swells, and when exposed to air with relatively low humidity, it shrinks.
If shrinkage could occur without the use of reinforcing bars, cracking would not occur, but in most cases, structural support requirements make this impossible. However, these characteristics result in concrete structures lacking the flexibility to move in response to environmental or volume changes. Understand what your contractor is doing with respect to each of the items listed above and you will get a concrete good job. Settlement cracks typically occur in situations where a void is created in the ground below the concrete surface.
Even the American Concrete Institute does not have standards or recommendations that give a yes or no answer as to which cracks need repair based on width and other factors. Careful timing is essential to ensure that the concrete liquefies again under the action of the vibrator and that the cracks are completely closed. These types are the result of the bleeding and segregation process that occurs when fresh concrete is placed. If left untreated, the peeling of joints, as well as the ingress of water and other materials, can reduce the life of the concrete structure.
Concrete usually provides passive protection to steel, as it forms a protective oxide coating around it in an alkaline environment. It can maintain the curing process by maintaining the wet condition of the newly laid concrete by wet curing. On sunny or windy days, where the top of the slab dries faster than the bottom, the top of the concrete surface may become crisp. Depending on the temperature difference and the deformation capacity of the concrete, differential thermal deformations can cause the concrete to form cracks due to early thermal shrinkage.
By using the procedures in this publication and exercising proper care, you will get the best performance from your Holcim concrete. Cracks that are identified as small and fine (less than 0.3 mm wide), are generally considered acceptable as part of a smaller settlement depending on the purpose and intent of the concrete structure, the environment in which it is placed, the service life and the durability design. Reducing the pH of concrete by carbonation or the ingress of chlorides (salt), which are the most common causes of concrete corrosion, causes the passive film of steel to degrade. .